1) Field of the Invention
The invention relates to a method of mixing pulp components in the manufacture of paper, according to which method a first pulp component is fed along an outer tube to a mixing point, the other pulp components being fed along at least one inner tube arranged inside the outer tube to the mixing point, whereby flows of said pulp components combine at the mixing point.
Further, the invention relates to an arrangement for mixing pulp components in the manufacture of paper, which arrangement comprises an outer tube for leading a first pulp component to a mixing point and at least one inner tube arranged inside the outer tube, whereby the inner tube is arranged substantially in parallel with the outer tube at least by its outer end, and in which arrangement a second pulp component is arranged to be led from the inner tube to the mixing point in such a way that flows of the pulp components to be fed are arranged to combine at the mixing point.
2) Description of Related Art
There are several points in different processes of paper manufacture where different mixtures of fluid and desired pulps and other substances have to be mixed with each other. For example, fiber pulp is thickened and diluted as required by feeding fiber suspension or dilution water thereto prior to leading it to the head box of the paper machine. Required additives, such as coloring, retention and filling agents, may also be mixed into the main flow. The fluids may be mixed using different tube mixers or by means of mechanical mixers in a tank. Cones and different tube joints, such as T and Y joints, are utilized for the mixing taking place in a tube. Further, additives may be mixed into a fluid flow by feeding them as jets against the main flow in the direction of the radius. A problem with known solutions is, however, that the mixing does not take place in a satisfactory way, which causes various problems at the following stages of the process. For example, variation in the consistency of the fiber flow as a result of inferior mixing in the dilution or thickening easily leads to problems in the product quality.
An object of the present invention is to provide a novel and improved solution for mixing pulp components in a tube.
The method according to the invention is characterized by generating at the mixing point turbulence in the flows of the pulp components to be mixed by means of an inner tube end having a wave-like cross-section, and by guiding the turbulence generated in this way by means of form parts positioned in the vicinity of the inner tube end and arranged on the inner surface of the outer tube, the greatest cross-section of the form parts being after the outermost end of the inner tube in the direction of flow.
Further, the arrangement according to the invention is characterized in that the outer end of the inner tube has a wave-like cross-section, whereby it is arranged to generate turbulence in the flows to be mixed; that in connection with the mixing point, there are form parts arranged on the inner surface of the outer tube for guiding the generated turbulence; and that the greatest cross-section of the form parts is after the outermost end of the inner tube in the direction of flow.
The essential idea of the invention is that the pulp components are fed to the mixing point of the pulp components along tubes arranged inside each other. For the purpose of mixing, the cross-section of the inner tube end is made wave-like, whereby it generates turbulence in the pulp component flows. The mixing effect of the turbulence is intensified by means of form parts arranged on the inner surface of the outer tube in connection with the mixing point, which form parts guide and intensify the generated turbulence. Still further, the essential idea of a preferred embodiment of the invention is that the cross-section of a form part changes in the direction of the radius and periphery of the outer tube in the direction of flow, whereby it changes from a linear front edge to a sector of a circle and back to a linear rear edge.
An advantage of the invention is that the pulp components to be mixed can be mixed with each other more efficiently and reliably than before, whereby the earlier problems at the following stages of the manufacturing process, resulting from the mixing, can be avoided. This naturally improves the efficiency of the process and enables manufacture of products having uniform quality. Moreover, good mixing even allows smaller amounts of additional components to be mixed into the main flow, because now inferior mixing does not have to be compensated for with oversized feed of components. Form parts according to the invention allow intensification of the turbulence generated by means of the inner tube end having a wave-like cross-section, more efficient mixing of the pulp components being consequently achieved. Further, what is known as the ejector effect can be reduced by means of form parts. As a form part is formed in such a way that its cross-section area begins from zero and ends at zero, the fibers or other component parts do not adhere to it but it remains clean easily. Combining an inner tube having a suitable wave-like form and suitable dimensions with form parts suitably dimensioned and appropriately positioned relative to the end of the inner tube allows the tailoring of a mixer giving the best possible result in each particular case.